Why? As paying clients, shouldnt our requested be respected with at least some effort and at least an explanation of why not? Sure seems like no effort has gone into it. Its a pretty documented and standard protocol.

We have not had the time to investigate CalDAV yet. We are a small company with limited resources and we have been focusing on other things, but it is on our to-do list and we will get to it eventually. Sorry.

I am a user of 2Do and have used toodledo (as a paid customer) for syncching various devices in the past. Now I use calDav and would not be renewing, unless there is support for calDav, which would let me accessing my tasks data on the web.

¿3 years? There is an obvious reason: caldav is OPEN. If you use CalDav, you are free to sync with almost anything: gcal, ical, tons of Open SOurce and free software. You should tell the reasons clearly, because they're your cliens and are paying you.